1. Field of the Invention
This invention relates to a motor structure usable as a driving source to cause a linear movement such as a head actuator of a floppy disc driving device (hereinafter referred to as an FDD), and more particularly, to a motor structure where a pair of sliding parts engage each other to convey a driving force, and further to a motor structure equipped with means for preventing its linearly moving output shaft from rotating.
1. Description of the Prior Art
In a linear actuator using a two-phase synchronous motor such as an actuator of an FDD, it is well known to use screw means to convert a moving direction. A screw structure using a ball is employed to reduce a frictional loss caused therein and attain high output and high efficiency, as disclosed in Japanese Utility Model Laid-Open No. 62-3080. Therefore, such an actuator structure is expensive because of installing balls, and so it may be applied only in a limited technical field. On the other hand, a screw structure without balls is inexpensive, but it is remarkably inferior in conversion efficiency due to a large frictional loss. Additionally, it is remarkably inferior in durability because of a large abrasion loss of resin of the screw, and then it is far from an actual use. Such abrasion occurs markedly, in particular, when a range of working temperature becomes wide. Referring to another problem in this prior art, means for preventing an output shaft from rotating is installed in a device receiving an output from a motor so that the device requires a mounting space therefor. It is not preferable for downsizing of the equipment. Further, since it results in controlling an output shaft movement precisely by using two or more regulating parts, such control is too complicated.
Although it is generally known that a preferable result such as reduction in abrasion loss can be obtained by using a resin for a female screw and metal for a male screw in a motion conversion mechanism with a screw, it can be barely proved, in substance, that the so-called scuffing or seizure of the sliding parts is hardly caused to stabilize the sliding parts by selecting, as the materials for the sliding parts, those differing in hardness so as to minimize the friction as much as possible; and the fact is that each determines after examination to which part the resin is used, or which resin is suitable therefor according to the purpose of use. Since the output shaft is provided with many sliding parts, it is apt to hit itself against a bench or another part at handling. Consequently, the output shaft must be formed of a material strong enough to hold, preferably formed of a metal.